Method of sealing leaky well tubing



Oct. 27, 1964 C. TAPSCOTT, JR, ETAL METHOD OF SEALING LEAKY WELL TUBING Filed April 4. 1962 INVENTORS CARL TAPSCOTT,JR

. .HA ES,JR.

v BY

A T TORNE VS United States Patent 3,154,144 METHOD OF SEALING LEAKY WELL TUBING Carl Tapscott, Jr. and Victor L. Hayes, Jr., ()dessa, Tex., assignors t Phillips Pen'oleum Company, a corporation of Delaware Filed Apr. 4, 1962, Ser. No. 185,027 5 Claims. (iCl. 166-14) This invention relates to a method for sealing leaky well tubing while in position in the well.

Gas is produced from deep wells in which the tubing pressure runs as high as 4,000 p.s.ig. and even higher. In such walls the maximum pressure that can be safely tolerated at the top of the casing at the well head is about 3200 to 3600 p.s.i.g. Also, higher pressures than this endanger the packer set between the tubing and the casing near the producing formation. This packer seals off the annulus so that the same can be filled with a liquid to help protect the tubing from the pressure therein. Because of the tension and stress on the tubing, minute leaks develop in the threads of the tubing joints and gas escapes from the tubing into the annulus so as to eventually equalize the pressure inside and outside of the tubing and raise the annulus pressure to the danger point. In operation of these deep wells, it is customary practice to bleed down the casing pressure (within the annulus) to about 3,000 p.s.i., thereby establishing a pressure differential across the tubing of about 1,000 p.s.i. When the casing or annulus pressure builds up to 3600 or 3700 pounds in 24 hours due to leakage thru the tubing, it is necessary to take steps to reduce the leakage. One method is to pull the tubing and completely work over the joints. Another method is to replace the tubing string at a cost of about $50,000 to $170,000. In a period of 6 years of production in 16 deep wells in the Ellenberger sand in West Texas (a depth of 16,000 ft.) 12 tubing strings out of the 16 have been replaced due to excessive leakage. A tubing string may last from three or four months to more than six years. The wells are produced at a rate of IOMM c.f.d. of natural gas.

This invention is concerned with a method of plugging leaks in tubing in wells without removing the tubing from the well.

Accordingly, it is an object of the invention to provide a method for sealing leaky tubing in place in a well. Another object is to provide an economical, efficient, and rapid method for sealing leaky tubing in a deep gas well. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises injecting bundles of unpolished cotton fiber and water into a tubing string in a well with an existing pressure differential between the tubing and the surrounding annulus of about 100 to 1000 p.s.i. and passing the resulting aqueous suspension of fibers along the tubing until the same reaches the leak and seals it. Leaky tubing strings in several deep wells in the Ellenberger sand have been successfully plugged by this method.

A more complete understanding of the invention may be had from a consideration of the accompanying schematic drawing which is an elevational view in partial section thru a deep well equipped for producing gas and for operation of the method of the invention.

Referring to the drawing a deep well 10 penetrates a gas formation 12 and is provided with a casing 14 which is perforated at 16 within stratum 12. A tubing string 18 extends from a level adjacent stratum 12 thru a seal 20 at the well head. A packer 22 seals off the well annulus 24 from the gas pressure in the well. A packer fluid, such as drilling mud, is maintained in the annulus above packer 22 to the level 26. A lubricator 28 above the well head is provided between valves 30 and 32. A production line 34 connects with tubing 18 thru the Well head and a bleed-off line 36 connects with the casing. Line 38 connects with tubing 18 below valve 32 for injection of water under the pressure of a pump (not shown).

To illustrate the invention a bundle of unpolished cotton string, commonly termed kite string amounting to 300 feet and cut into 2 to 3 inch lengths, and bound with toilet tissue to hold the bundle together until immersed in the water, was introduced into lubricator 28 by opening valve 30 while valve 32 was closed and then closing valve 30 and opening valve 32. The valve in line 34, of course, was closed and a barrel of water was injected under pressure thru line 38. The pressure differential between the tubing and easing during this treatment was in the range of to 1000 p.s.i., and the pressure dilferential was decreasing rather rapidly during the treatment. Prior to the treatment a 1,000 p.s.i. differential would equalize in about 10 minutes, i.e., with a tubing pressure of 4,000 p.s.i. and a pressure of 3,000 p.s.i. in the annulus, it required only 10 minutes for the pressures to equalize. The pressure differential desired was readily maintained by cracking the valve in line 36 to reduce annulus pressure.

Successive unit injections of a bundle of cotton cord and barrel of water were continued and between the 3rd and 4th unit injection a typical indication of plugging of the tubing leak Was obtained with a sharp diminishing of loss of pressure differential.

During this treatment it was intended to follow the cord plugging step with injection of sodium silicate in order to harden the cord in the plugged leak. However, there was a sharp drop in the weather temperature and the master valves at the well head began to freeze up and this made it impossible to continue the treatment and the well was immediately blown down to remove the cord and water. When the gas flow cleaned up, the well was placed on regular flow at a rate of 10MM c.f.d. After three weeks of service the tubing was functioning well in that a steady casing-tubing pressure diiferential of 500 p.s.i. could be maintained. A subsequent second similar plugging job on well A has lasted 5 months and is still holding.

Another gas well in the Ellenberger field, designated well B was given a plugging treatment of 3 units, each unit consisting of one bundle of unpolished string or cord 2 to 3" in length bound with toilet tissue and one barrell of water. The tubing-casing pressure diiferential was approximately 1,000 p.s.i. at the start of treatment and 800 p.s.i. at completion. The well was given an injection of 4 barrels of grade 40 sodium silicate after the injection of the third barrel of water and string. The sodium silicate Was-held in the tubing 4 hours before blow-down which cleaned up the well is a short time. Fiber dispersion in the return flow of silicate was good. The well was shut-in 20 hours after blow-down. During the shut-in period, casing pressure held steadily at 3,000 p.s.i. and with tubing pressure at 3800 p.s.i. After 20 hours the well was on stream at a rate of approximately 10MM c.f.d. Casing pressure immediately began to rise due to temperature increase in the well bore and after bleeding oif the casing pressure repeatedly, it stabilized at 3250 p.s.i. and held at this pressure for several weeks.

The foregoing tests clearly demonstrate that the sodium sillicate treatment is unnecessary and is time consuming so that its elimination is of considerable economic significance.

When well B required subsequent plugging treatment to that disclosed, it was given a similar treatment without the addition of sodium silicate and this second treatment lasted more than two months. A third treatment was given the well to plug a leak in the tubing and this Patented Oct. 27, 1964 has lasted approximately two months and the well is still maintaining a good differential pressure between the casing and the tubing without further need of treatment.

Well A required subsequent treatment and was given the cotton string-barrel of water unit treatment to plug the leak and the plug has lasted for a period of about five months without requiring replugging.

In all of the above treatments the amount of cord utilized in each unit (1 bundle of cord-one barrel of water) was about 300 ft. However, the amount may be varied in the range of 150 to 400 feet cut into short lengths in the range of about 1 to 6 inches.

Prior to treatment with unpolished cotton string or cord and water, an attempt was made to plug leaks in well A, one of the deep Ellenberger wells, using sodium silicate injections. In one treatment, 165 gallons of undiluted grade 40 sodium silicate was injected and it was certain that the volume of silicate injected was sufficient to reach and enter the tubing leak. The pressure before and after the squeeze treatment with sodium silicate did not reflect any appreciable difierence or indicate any improvement. After the treatment the casing pressure rose from 3600 p.s.i. to 4000 p.s.i. (equal to the tubing pressure) in a period of 1 hour.

After failing to plug well A with sodium silicate, an attempt was made to plug the tubing of well B by treating the same with manila rope fiber and sodium silicate. The rope was cut into short lengths of about 1 /3 to 2" and injected with a barrel of water. After injection of 3 units (one barrel of water and several hundred inches of rope fibers) an additional barrel of water without rope was injected as a flush, and a 4-barrel slug of undiluted grade 40 sodium silicate then was injected. The casing pressure was reduced to obtain a 400 p.s.i. tubing-casing pressure differential prior to starting the treatment. The plugging effect of the leak was realized while injecting the first unit and before injecting the second unit, the casing pressure was further reduced to provide a 500 p.s.i. squeeze differential. At the conclusion of a 4 /2 hour wait, timed from the start of the silicate injection, the well was blown-down without undue difficulty. The well was returned to flow one hour after blow-down. Before treatment, casing and tubing pres sure would stabilize from a pressure differential of about 800 p.s.i. in about two hours. After treatment the casing pressure was bled to 3200 p.s.i. and it rose in approximately one day to 3500 p.s.i. with tubing pressure holding steady at 3800 p.s.i. This indicated a partial plug of the tubing leak. Several days later this well (well B) was given the cotton string-barrel of water treatment referred to above to effect a complete plugging of the leak.

An attempt was made to seal or plug the tubing of well A prior to the first plugging of a tubing leak therein with the cotton string-barrel of water squeeze treatment. The procedure followed was similar to that used on well B using rope fiber (l /2" long) and water followed by sodium silicate. After injection of 4 units, a slug of 3 barrels of undiluted sodium silicate was injected. During the treatment at least 100 p.s.i. pressure differential was periodically established across the tubing by cracking the casing bleed-oif valve (in line 36). The well was shut in for 4 hours following the silicate injection. The tubing was then blown down to establish clean flow in 7 minutes.

The well was put back on line about 17 hours later and had to be shut in to clean rope fiber out of the valve in line 34. When the Well was again put back on line, tubing and casing pressure stabilized at 3700 p.s.i. within one hour. Casing pressure was then bled to 3500 p.s.i. and in one hour the tubing-casing pressures had again stabilized at 3700 p.s.i.

About one month later a similar attempt was made to seal the tubing of well A using sodium silicate in place of water to carry the rope thru the tubing. An adequate seal was effected but lasted only about 2 /2 hours. Dispersion of fiber was not as good as with water.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim:

1. In a deep well having a jointed tubing and a casing extending to a deep gas stratum producing gas at a pressure of at least 1000 p.s.i., wherein the annulus between said tubing and casing is sealed off just above said stratum and the well head pressure in said annulus is maintained at least 50 p.s.i. below the pressure in said tubing, and wherein a leak of gas thru a joint of said tubing to said annulus occurs, the method of sealing off said leak comprising introducing relatively short pieces of unpolished cotton fibers into said tubing admixed with water; and flowing under substantial pressure the resulting mixture down the inside of said tubing while maintaining the pressure in the annulus surrounding said tubing at least 50 p.s.i. less than in said tubing so as to cause water and fibers to flow into said leak, thereby plugging said leak.

2. The method of claim 1 wherein said fibers are in the form of string of a length in the range of 1 to 6 inches.

3. The method of claim 2 wherein said string is introduced in bundles held together by weak absorbent paper which, when wet, disintegrates in the tubing turbulence caused by descent of the water thru the tubing.

4. The method of claim 1 wherein said fibers are in the form of string, said string is in readily dispersible bundles when in an aqueous medium, a unit of 150 to 400 feet of string cut in lengths of 1 to 6 inches is injected into said tubing in about one barrel of water, and successive units and barrels of water are injected until plugging is effected.

5. A process for plugging small leaks in a well tubing within a casing in a well extending to a deep gas formation which comprises maintaining a gas pressure differential between said tubing and the surrounding annulus in the range of to 1500 p.s.i. with leakage of gas from said tubing to said annulus and reduction of said differential; injecting successive units of water and unpolished cotton string cut in 1 to 6 inch pieces in an amount in the range of to 400 feet per barrel of water into said tubing, thereby effecting leakage of water into said annulus from said tubing, until plugging is indicated by a steady pressure differential; thereafter terminating inection; and allowing pressure in said tubing to blow out injected water and excess string.

References Cited in the file of this patent UNITED STATES PATENTS 1,548,012 Dunn July 28, 1925 

1. IN A DEEP WELL HAVING A JOINTED TUBING AND A CASING EXTENDING TO A DEEP GAS STRATUM PRODUCING GAS AT A PRESSURE OF AT LEAST 1000 P.S.I., WHEREIN THE ANNULUS BETWEEN SAID TUBING AND CASING IS SEALED OFF JUST ABOVE SAID STRATUM AND THE WELL HEAD PRESSURE IN SAID ANNULUS IS MAINTAINED AT LEAST 50 P.S.I. BELOW THE PRESSURE IN SAID TUBING, AND WHEREIN A LEAK OF GAS THRU A JOINT OF SAID TUBING TO SAID ANNULUS OCCURS, THE METHOD OF SEALING OFF SAID LEAK COMPRISING INTRODUCING RELATIVELY SHORT PIECES OF UNPOLISHED COTTON FIBERS INTO SAID TUBING ADMIXED WITH WATER; AND FLOWING UNDER SUBSTANTIAL PRESSURE THE RESULTING MIXTURE DOWN THE INSIDE OF SAID TUBING WHILE MAINTAINING THE PRESSURE IN THE ANNULUS SURROUNDING SAID TUBING AT LEAST 50 P.S.I. LESS THAN IN SAID TUBING SO AS TO CAUSE WATER AND FIBERS TO FLOW INTO SAID LEAK, THEREBY PLUGGING SAID LEAK. 